1) Field of the Invention
The present invention relates to a delay line device used to delay signal transmission in a computer, an instrumentation or the like and more particularly to a delay line device capable of adjusting a delay time.
2) Description of the Prior Art
As an example of a delay line device, there is one using a distributed constant circuit. FIG. 1 shows a delay line device of the so-called microstrip type in the above category. This delay line device comprises a meandering strip line conductor 31 formed on a main surface of a dielectric substrate 30 and a grounding electrode layer (not shown) formed on an opposite surface thereof. The length of the strip line conductor 31 determines a delay time obtained between an input lead terminal 32 and an output lead terminal 33. In order to change the delay time in this delay line device after manufacturing, an intermediate tap lead terminal 34 is connected to the strip line conductor 31 between the input and output lead terminals 32 and 33 and is used as an output terminal. The delay time can be adjusted by varying the position at which the intermediate tap lead terminal 34 is connected to the strip line conductor 31.
However, in the above delay line device, it is impossible to adjust the delay time after it is mounted on a printed circuit board since the positions of the input and output terminals are determined by the delay time. In addition, since one of the three lead terminals 32, 33 and 34 is not used after mounting, it has an undesired capacitance or acts as a stub which causes reflection of a signal. Further, when the strip line conductor 31 is meandering as shown in FIG. 1 , the position at which the intermediate tap lead terminal 34 is to be connected to the strip line conductor 31 is limited to the portions indicated by A. This prevents fine adjustment of the delay time.